Optical Terminology
192
What is light to photography?
What is ‘light’?
Light is a physical phenomenon which
involves creating vision by stimulating the
optic nerves, and can be broadly defined
as a type of electromagnetic wave.
Types of electromagnetic radiation vary
according to wavelength. Starting from
the shortest wavelengths, electromagnetic
radiation can be classified into gamma
rays, X rays, ultraviolet light rays, visible
light rays, infrared light rays, far-infrared
light rays, microwave radiation, ultra
short wave radiation (VHF), short wave
radiation, medium wave radiation (MF)
and long wave radiation. In photography,
the most utilised wavelengths are in the
visible light region (400nm~700nm).
Since light is a type of electromagnetic
radiation, light can be thought of as a
type of wave in the category of “light
waves.” A light wave can be regarded as
Figure-1 Approaching the human eye
Frequencies
Wavelength
103
(1kHz)
VLF
(Ultra-long wave)
VLF
104
LF
(Long wave)
LF
105
MF
106
(1MHz)
MF
(Medium wave)
km
Radio
waves
HF
an electromagnetic wave in which an
electric field and magnetic field vibrate at
right angles to each other in a plane
perpendicular to the direction of propagation. The two elements of a light wave
which can actually be detected by the
human eye are the wavelength and
amplitude. Differences in wavelength are
sensed as differences in colour (within
the visible light range) and differences in
amplitude are sensed as differences in
brightness (light intensity). The third
element which cannot be detected by the
human eye is the direction of vibration
within the plane perpendicular to the
light wave’s direction of propagation
(polarized light).
Basic light-related phenomena
Refraction
A phenomenon whereby the propagation
direction of a ray of light changes when
the light passes from one medium such as
a vacuum or air into a different medium
such as glass or water, or vice versa.
Figure-3 Light Refraction
Incident
angle
i
characteristics of the lens or prism cause
the index of refraction to vary depending on the wavelength, thus dispersing
the light. This is also sometimes referred
to as colour dispersion.
Extraordinary partial dispersion
The human eye can sense monochromatic light wavelengths within the
range of 400nm (purple) to 700nm (red).
Within this range, the difference in index
of refraction between two different
wavelengths is called partial dispersion.
Most ordinary optical materials have
similar partial dispersion characteristics.
However, partial dispersion characteristics differ for some glass materials,
such as glass, which has larger partial
dispersion at short wavelengths, FK glass
which features a small index of refraction and low dispersion characteristics,
fluorite, and glass which has larger
partial dispersion at long wavelengths.
These types of glass are classified as
having extraordinary partial dispersion
characteristics. Glass with this property is
used in apochromatic lenses to
compensate chromatic aberration.
Figure-4 Light Dispersion by A Prism
HF
(Short wave)
Ordinary optical glass
Special optical glass
107
Extraordinary
partial dipersion
VHF
(Ultra-short wave)
VHF
108
UHF
Micro
109
(1GHz)
SHF
1010
SHF
(Centimeter wave)
EHF
1011
EHF
(Millimeter wave)
mm
Sub millimeter
wave
Far infrared
1eV
1013
1014
Visible light rays
m
Red
0.64
Orange
0.59
Yellow
0.55
Green
0.49
Blue
0.43
Violet
0.38
0.77
Near infrared
Ultraviolet
1015
Vacuum
ultraviolet
1016
1017
1keV
1018
1
X rays
1019
1020
1MeV
1021
γ rays the
10 human eye
Figure-2 Approaching
22
1023
Amplitude
1GeV
Electric field
Wavelength
Magnetic field
Direction of propagation
193
Y
R
B
Y
B
r
10
(1THz)
1m
1nm
Refraction
angle
12
Infrared
R
R
Y
B
UHF
(Extremely
ultra-short wave)
Index of refraction
A numerical value indicating the degree
of refraction of a medium, expressed by
the formula n = sin i/sin r. “n” is a
constant which is unrelated to the light
ray’s angle of incidence and indicates
the refractive index of the refracting
medium with respect to the medium
from which the light impinges.
For general optical glass, “n” usually
indicates the index of refraction of the
glass with respect to air.
Reflection
Reflection differs from refraction in that it
is a phenomenon which causes a portion
of the light striking the surface of glass or
other medium to break off and propagate
in an entirely new direction. The direction
of propagation is the same regardless of
wavelength. When light enters and leaves
a lens which does not have an antireflection coating, approximately 5% of
the light is reflected at the glass-air
boundary. The amount of light reflected
depends on the glass material’s index of
refraction.→Coating (P.174)
Figure-5 Light Reflection
Normal reflection
Abnormal reflection
Center line
Dispersion
A phenomenon whereby the optical
properties of a medium vary according
to the wavelength of light passing
through the medium. When light enters
a lens or prism, the dispersion
Flat surface, flat smooth surface
Rough surface
Diffraction
A phenomenon in which light waves
pass around the edges of an object and
enter the shadowed area of that object,
caused because of the wavelike nature of
light. Diffraction in a photographic lens
is known for causing flare (diffraction
flare) which occurs when light rays bend
around the edges of the diaphragm.
Although diffraction flare tends to
appear when the diaphragm diameter is
smaller than a certain size, it actually
depends not only on the diameter of the
diaphragm but also on various factors
such as the wavelength of the light, the
lens’s focal length and the aperture ratio.
Diffraction flare causes reductions in
image contrast and resolution, resulting
in a soft image. The laminated
diffraction optical elements developed by
Canon control the direction of the light
by intentionally creating diffraction.
with the optical axes of all other lens
elements. Particularly in zoom lenses,
which are constructed of several lens
groups that move in a complex manner,
extremely precise lens barrel construction
is necessary to maintain proper optical
axis alignment.
Paraxial ray
A light ray which passes close to the
optical axis and is inclined at a very small
angle with respect to the optical axis. The
point at which paraxial rays converge is
called the paraxial focal point. Since the
image formed by a monochromatic
paraxial ray is in principle free of aberrations, the paraxial ray is an important
factor in understanding the basic
operation of lens systems.
Principal ray
A light ray which enters the lens at an
angle at a point other than the optical
axis point and passes through the center
of the diaphragm opening. Principal
light rays are the fundamental light rays
used for image exposure at all diaphragm openings from maximum
aperture to minimum aperture.
Figure-6 Light Diffraction
Straight advancing light Center maximum
Diffracted
light
Aperture
Diffraction phenomenon
seen on waters surface
Incident light
First light ring First shadow ring
Light intensity distribution
Optical terminology related to
light passing through a lens
Figure-7 Optical Terminology Related To Light
Passing Through A Lens
Parallel pencil of rays
Effective
aperture
Optical
axis
Focal
point
Aperture
diameter
Aperture
Distance of
incidence
Paraxial
ray
Paraxial focal point
Principal ray
Optical axis
A straight line connecting the center
points of the spherical surfaces on each
side of a lens. In other words, the optical
axis is a hypothetical center line
connecting the center of curvature of each
lens surface. In photographic lenses
comprised of several lens elements, it is of
utmost importance for the optical axis of
each lens element to be perfectly aligned
Parallel pencil of rays
A group of light rays traveling parallel to
the optical axis from an infinitely far point.
When these rays pass through a lens, they
converge in the shape of a cone to form a
point image within the focal plane.
Ray tracing
Use of geometrical optics to calculate
the condition of various light rays
passing through a lens. Calculations are
performed using powerful computers.
Aperture/effective aperture
The aperture of a lens is related to the
diameter of the group of light rays
passing through the lens and determines the brightness of the subject
image formed on the focal plane. The
optical aperture (also called the effective
aperture) differs from the real aperture
of the lens in that it depends on the
diameter of the group of light rays
passing through the lens rather than the
actual lens diameter. When a parallel
pencil of rays enters a lens and a group
of these rays passes through the
diaphragm opening, the diameter of this
group of light rays when it enters the
front lens surface is the effective
aperture of the lens.
Stop/diaphragm/aperture
The opening which adjusts the diameter
of the group of light rays passing through
the lens. In interchangeable lenses used
with single lens reflex cameras, this
mechanism is usually constructed as an
iris diaphragm consisting of several blades
which can be moved to continuously vary
the opening diameter. With conventional
SLR camera lenses, the aperture is
adjusted by turning an aperture ring on
the lens barrel. With modern camera
lenses, however, aperture adjustment is
commonly controlled by operating an
electronic dial on the camera body.
Circular aperture diaphragm
With normal aperture diaphragms,
closing the aperture causes its shape to
become polygonal. A circular aperture
diaphragm, on the other hand,
optimises the shape of the blades to
achieve a nearly perfect circle even
when considerably stopped down from
the maximum aperture. Photography
with a lens that is equipped with a
circular aperture diaphragm achieves a
beautiful blur effect for the background,
because the point source is circular.
Automatic diaphragm
The general diaphragm operation system
used in SLR cameras, referring to a type of
diaphragm mechanism which remains
fully open during focusing and
composition to provide a bright viewfinder
image, but automatically closes down to
the aperture setting necessary for correct
exposure when the shutter button is
pressed and automatically opens up again
when the exposure is completed. Although
conventional lenses use mechanical
linkages for controlling this automatic
diaphragm operation, EF lenses use
electronic signals for more precise control.
You can observe this instantaneous
aperture stop-down operation by looking
into the front of the lens when the shutter
is released.
Distance of incidence
Distance from the optical axis of a
parallel ray entering a lens.
Entrance pupil/exit pupil
The lens image on the object side of the
diaphragm, i.e. the apparent aperture seen
when looking from the front of the lens, is
called the entrance pupil and is equivalent
in meaning to the lens’ effective aperture.
The apparent aperture seen when looking
194
Figure-8 Pupils and Angular Aperture
Entrance pupil Exit pupil
Angular aperture
Angular aperture
Image
point
Object point
from the rear of the lens (the lens image on
the image side of the diaphragm), is called
the exit pupil. Of the light rays from a
certain subject point, the effective light rays
which actually form the image create a cone
of light rays with the subject point being the
point of the cone and the entrance pupil
being the base of the cone. At the other end
of the lens, the light rays emerge in a cone
shape with the exit pupil forming the base
of the cone and the point of the cone falling
within the image plane. The entrance and
exit pupils have the same shape as the
actual diaphragm and their size is directly
proportional to that of the diaphragm, so
even if the construction of the lens system is
not known, it is possible to graphically
illustrate the effective light rays which
actually form the image as long as the
positions and sizes of the entrance and exit
pupils are known. Thus, knowledge of the
entrance and exit pupils is indispensable
when considering performance factors such
as the total amount of light entering the
lens, the manner in which the image blurs
and aberrations.
Angular aperture
The angle between the subject point on
the optical axis and the diameter of the
entrance pupil, or the angle between the
image point on the optical axis and the
diameter of the exit pupil.
Flange back and back focus
Flange back
Distance from the camera’s lens mount
reference surface to the focal plane (film
plane). In the EOS system, flange back
is set at 44.00 mm on all cameras.
Flange back is also referred to as
flange-focal distance.
Back focus
With a lens focused to infinity, the distance
along the optical axis from the apex of the
rearmost glass surface to the focal plane is
called back focus. Wide-angle lenses with a
short back focus cannot be used on SLR
cameras that use a mirror that swings up
before exposure because the lens will
obstruct the mirror movement. Wide-angle
lenses for SLR cameras generally employ a
retrofocus design which allows a long back
focus. The compact size of the quick-return
mirror on the EF-S lens compatible digital
SLR cameras makes it possible to design
lenses like the dedicated EF-S 60mm f/2.8
Macro USM, EF-S 10-22mm f/3.5-4.5 USM,
EF-S 17-55mm f/2.8 IS USM and EF-S 1855mm f/3.5-5.6 II USM lenses with a
shorter back focus than in other EF lenses.
object-side focal point if it is the point at
which light rays entering the lens parallel
to the optical axis from the focal plane
side converge on the object side of the
lens.
Focal length
When parallel light rays enter the lens
parallel to the optical axis, the distance
along the optical axis from the lens’
second principal point (rear nodal point)
to the focal point is called the focal length.
In simpler terms, the focal length of a lens
is the distance along the optical axis from
the lens’ second principal point to the focal
plane when the lens is focused at infinity.
Figure-11 Focal Length of Actual
Photographic Lens
Focal length
h'
Focal point and focal length
Focal point, focus
When light rays enter a convex lens
parallel to the optical axis, an ideal lens
will converge all the light rays to a single
point from which the rays again fan out in
a cone shape. This point at which all rays
converge is called the focal point. A
familiar example of this is when a
magnifying glass is used to focus the rays
of the sun to a small circle on a piece of
paper or other surface; the point at which
the circle is smallest is the focal point. In
optical terminology, a focal point is further
classified as being the rear or image-side
focal point if it is the point at which light
rays from the subject converge on the film
plane side of the lens. It is the front or
Figure-10 Focal Point (single lens element)
Principal point
The focal length of a thin, double-convex,
single-element lens is the distance along
the optical axis from the center of the lens
to its focal point. This center point of the
lens is called the principal point. However,
since actual photographic lenses consist of
combinations of several convex and
concave lens elements, it is not visually
apparent where the center of the lens
might be.
The principal point of a multi-element
lens is therefore defined as the point on
the optical axis at a distance equal to the
focal length measured back toward the
lens from the focal point. The principal
point measured from the front focal point
is called the front principal point, and the
principal point measured from the rear
focal point is called the rear principal
Figure-12 Principal point
Rear principal point
Parallel light rays
a
n'
n
Focal
point
Figure-9 Flange Back and Back Focus
h
h'
b
Image focal
point
Front principal point Rear principal point
Focal length
(First principal point) (Second principal point)
Fig.12-A
Convex lens
Object space
Image space
Fig.12-B
Telephoto type
Focal
Point
Rear principal point
Object focal point
(Front focal point)
Image focal point
(Rear focal point)
Focal length
Concave lens
Fig.12-C
Retrofocus (Inverted telephoto type)
Focal
point
Back focus
Flange back
Image focal point
Object focal point
Focal length
Mount reference surface Focal plane
Rear principal point
195
Fig.12-D
point. The distance between these two
principal points is called the principal
point interval.
diagonal of the APS-C sized image
sensor of EF-S compatible digital SLR
cameras.
Front principal point/rear principal
point
Angle of view
The area of a scene, expressed as an angle,
which can be reproduced by the lens as a
sharp image. The nominal diagonal angle
of view is defined as the angle formed by
imaginary lines connecting the lens’
second principal point with both ends of
the image diagonal (43.2mm). Lens data
for EF lenses generally includes the
horizontal (36mm) angle of view and
vertical (24mm) angle of view in addition
to the diagonal angle of view.
Light entering a lens from point a in
Figure-12-A refracts, passes through n and
n’ and arrives at b. When this occurs,
similar angles are generated between a-n
and n’-b with respect to the optical axis,
and points h and h’ can be defined as
where these angles intersect the optical
axis. These points, h and h’, are principal
points indicating the lens reference
positions with respect to the subject and
image. h is called the front principal point
(or first principal point) and h’ is called the
rear principal point (or second principal
point). In general photographic lenses, the
distance from h’ to the focal point (focal
plane) is the focal length. Depending on
the lens type, the front-rear relationship of
the principal points may be reversed, or h’
may fall outside of the lens assembly
altogether, but in any case the distance
from the rear principal point h’ to the focal
point is equal to the focal length.
*With telephoto type lenses, the rear
principal point h’ is actually positioned in
front of the frontmost lens element, and
with retrofocus type lenses h’ is positioned
to the rear of the rearmost lens element.
Image circle
The portion of the circular image
formed by a lens that is sharp.
Interchangeable lenses for 35mm
format cameras must have an image
circle at least as large as the diagonal of
the 24 x 36mm image area. EF lenses
therefore generally have an image circle
of about 43.2mm diameter. TS-E lenses,
however, are designed with a larger
image circle of 58.6mm to cover the
lens’s tilt and shift movements. EF-S
lenses feature a smaller image circle
than other EF lenses, to match the
Terms related to lens brightness
Aperture ratio
A value used to express image brightness,
calculated by dividing the lens’ effective
aperture (D) by its focal length (f). Since
the value calculated from D/f is almost
always a small decimal value less than I
and therefore difficult to use practically, it
is common to express the aperture ratio on
the lens barrel as the ratio of the effective
aperture to the focal length, with the
effective aperture set equal to 1. (For
example, the EF 85mm f/1.2L II USM lens
barrel is imprinted with 1 : 1.2, indicating
that the focal length is 1.2 times the effective
aperture when the effective aperture is
equal to 1.) The brightness of an image
produced by a lens is proportional to the
square of the aperture ratio. In general, lens
brightness is expressed as an F number,
which is the inverse of the aperture ratio
(f/D). F number
Figure-14 Lens Brightness
F number
f
D
D
f
Aperture ratio
brightness is inversely proportional to the
square of the F number, meaning that the
image becomes darker as the F number
increases. F number values are expressed
as a geometrical series starting at 1 with a
common ratio of √2, as follows: 1.0, 1.4, 2,
2.8, 4, 5.6, 8, 16, 22, 32, etc. (However, there
are many cases where only the maximum
aperture value deviates from this series.)
The numbers in this series, which may at
first seem difficult to become familiar
with, merely indicate values which are
close to the actual FD values based on the
diameter (D) of each successive diaphragm
setting which decreases the amount of
light passing through the lens by half.
Thus, changing the F number from 1.4 to
2 halves the image brightness, while going
the other direction from 2 to 1.4 doubles
the image brightness. (A change of this
magnitude is generally referred to as “1
stop”.) With recent cameras employing
electronic displays, smaller divisions of 1/2
stop or even 1/3 stop are used.
Numerical aperture (NA)
A value used to express the brightness or
resolution of a lens’ optical system. The
numerical aperture, usually indicated as
NA, is a numerical value calculated from
the formula nsinθ, where 2θ is the angle
(angular aperture) at which an object point
on the optical axis enters the entrance
pupil and n is the index of refraction of
the medium in which the object exists.
Although not often used with
photographic lenses, the NA value is
commonly imprinted on the objective
lenses of microscopes, where it is used
more as an indication of resolution than of
brightness. A useful relationship to know
is that the NA value is equal to half the
inverse of the F number. For example,
F 1.0 = NA 0.5, F 1.4 = NA 0.357, F2 = NA
0.25, and so on.
Focus and depth of field
D
Figure-13 Angle of view and image circle
Horizontal
36mm Image circle
Image circle
Vertical
24mm
Diagonal
43.2mm
Image circle
Angle
of view
Angle
of view
h
h'
Angle
of view
f
Image plane
F number
Since the aperture ratio (D/f) is almost
always a small decimal value less than
one and therefore difficult to use
practically, lens brightness is often
expressed for convenience’ sake as the
inverse of the aperture ratio (f/D), which is
called the F number. Accordingly, image
Focus, focal point
The focal point is the point where parallel
light rays from an infinitely far subject
converge after passing through a lens. The
plane perpendicular to the optical axis
which contains this point is called the focal
plane. In this plane, which is where the
film or the image sensor is positioned in a
camera, the subject is sharp and said to be
“in focus.” With general photographic
lenses consisting of several lens elements,
the focus can be adjusted so that light rays
196
from subjects closer than “infinity”
converge at a point in the focal plane.
Figure-15 Relationship Between the Ideal Focal
Point and the Permissible Circle of
Confusion and Depth of Field
Ideal focal point
Lens
Fro
n
of t de
fie pth
ld
De
pth
of
foc
Re
a
of r de
fie pth
ld
us
Permissible circle of confusion
Circle of confusion
Since all lenses contain a certain amount
of spherical aberration and astigmatism,
they cannot perfectly converge rays from a
subject point to form a true image point
(i.e., an infinitely small dot with zero area).
In other words, images are formed from a
composite of dots (not points) having a
certain area, or size. Since the image
becomes less sharp as the size of these
dots increases, the dots are called “circles
of confusion.” Thus, one way of indicating
the quality of a lens is by the smallest dot
it can form, or its “minimum circle of
confusion.” The maximum allowable dot
size in an image is called the “permissible
circle of confusion.”
Permissible circle of confusion
The largest circle of confusion which still
appears as a “point” in the image. Image
sharpness as sensed by the human eye is
closely related to the sharpness of the
actual image and the “resolution” of
human eyesight. In photography, image
sharpness is also dependent on the degree
of image enlargement or projection
distance and the distance from which the
image is viewed. In other words, in
practical work it is possible to determine
certain “allowances” for producing images
which, although actually blurred to a
certain degree, still appear sharp to the
observer. For 35mm single lens reflex
cameras, the permissible circle of confusion
is about 1/1000~1/1500 the length of the
film diagonal, assuming the image is
enlarged to a 5”×7” (12 cm × 16.5 cm)
print and viewed from a distance of 25~30
cm/0.8~1 ft. EF lenses are designed to
produce a minimum circle of confusion of
0.035 mm, a value on which calculations
for items such as depth of field are based.
197
Depth of field
The area in front of and behind a focused
subject in which the photographed image
appears sharp. In other words, the depth of
sharpness to the front and rear of the
subject where image blur in the focal
plane falls within the limits of the
permissible circle of confusion. Depth of
field varies according to the lens’ focal
length, aperture value and shooting
distance, so if these values are known, a
rough estimate of the depth of field can be
calculated using the following formulas:
Front depth of field = d·F·a2/(f2 + d·F·a)
Rear depth of field = d·F·a2/(f2 — d·F·a)
f: focal length F: F number d: minimum
circle of confusion diameter
a: subject distance (distance from the
first principal point to subject)
hyperfocal distance ×
shooting distance
Near point limiting
=
distance
hyperfocal distance +
shooting distance
Far point limiting
distance
=
50mm f/1.8
Aperture
Depth of focus at
maximum aperture
Aperture
Permissible
circle of confusion
Depth of
focus at f/5.6
hyperfocal distance shooting distance
Figure-16 Depth of Field and Depth of Focus
Minimum circle of confusion
Depth of focus
Depth of field
Near point
Front
depth of
focus
Front depth of field
Near point distance
Subject distance
Image
distance
Far point distance
Permissible
circle of confusion
f/1.8
hyperfocal distance ×
shooting distance
If the hyperfocal distance is known, the
following formulas can also be used:
In general photography, depth of field is
characterised by the following attributes:
a Depth of field is deep at short focal
lengths, shallow at long focal lengths.
b Depth of field is deep at small
apertures, shallow at large apertures.
c Depth of field is deep at far shooting
distances, shallow at close shooting
distances.
d Front depth of field is shallower
than rear depth of field.
Rear
depth
of field
Figure-17 Relationship Between Depth of
Focus and Aperture
f/5.6
(Shooting distance: Distance from focal plane to subject)
Far point
circle of confusion by the F number,
regardless of the lens focal length. With
modern autofocus SLR cameras, focusing
is performed by detecting the state of
focus in the image plane (focal plane)
using a sensor which is both optically
equivalent (1:1 magnification) and
positioned out of the focal plane, and
automatically controlling the lens to bring
the subject image within the depth of
focus area.
Rear
depth
of focus
Shooting distance
Focal plane
Depth of focus
The area in front of and behind the focal
plane in which the image can be
photographed as a sharp image. Depth of
focus is the same on both sides of the
image plane (focal plane) and can be
determined by multiplying the minimum
Hyperfocal distance
Using the depth of field principle, as a
lens is gradually focused to farther
subject distances, a point will eventually
be reached where the far limit of the
rear depth of field will be equivalent to
“infinity.” The shooting distance at this
point, i,e., the closest shooting distance
at which “infinity” falls within the depth
of field, is called the hyperfocal distance.
The hyperfocal distance can be
determined as follows:
Hyperfocal
distance =
f2
d•F number
f: focal length F: F number
d: minimum circle of confusion
diameter
Thus, by presetting the lens to the
hyperfocal distance, the depth of field will
extend from a distance equal to half the
hyperfocal distance to infinity. This
method is useful for presetting a large
depth of field and taking snapshots
without having to worry about adjusting
the lens focus, especially when using a
w i d e - a n g l e Photo-1 Hyperfocal Length Set
Condtion
lens.
(For
example, when
the EF 20mm
f/2.8 USM is set
to f/16 and the
shooting
distance is set
to the hyperfocal distance of approximately 0.7m/2.3ft, all subjects within
a range of approximately 0.4m/1.3ft from
the camera to infinity will be in focus.)
Lens aberration
Aberration
The image formed by an ideal photographic lens would have the following
characteristics:
a A point would be formed as a point.
b A plane (such as a wall) perpendicular
to the optical axis would be formed as a
plane.
c The image formed by the lens would
have the same shape as the subject.
Also, from the standpoint of image
expression, a lens should exhibit true
colour reproduction. If only light rays
entering the lens close to the optical axis
are used and the light is monochromatic
(one specific wavelength), it is possible to
realise virtually ideal lens performance.
With real photographic lenses, however,
where a large aperture is used to obtain
sufficient brightness and the lens must
converge light not only from near the
optical axis but from all areas of the
image, it is extremely difficult to satisfy
the above-mentioned ideal conditions due
to the existence of the following
obstructive factors:
V Since most lenses are constructed solely of lens elements with spherical surfaces,
light rays from a single subject point are
not formed in the image as a perfect point.
(A problem unavoidable with spherical
surfaces.)
V The focal point position differs for
different types (i.e., different wavelengths)
of light.
V There are many requirements related to
changes in angle of view (especially with
wide-angle, zoom and telephoto lenses).
The general term used to describe the
difference between an ideal image and the
actual image affected by the above factors
is “aberration.” Thus, to design a highperformance lens, aberration must be
extremely small, with the ultimate
objective being to obtain an image as
close as possible to the ideal image.
Aberration can be broadly divided into
chromatic aberrations, and monochromatic aberrations → Chromatic
aberration → Five aberrations of Seidel
Table-1 Lens Aberrations
Aberrations seen in the continuous spectrum
W Chromatic aberrations
VAxial chromatic aberration (longitudinal
chromatic aberration)
VTransverse chromatic aberration
(lateral chromatic aberration)
Aberrations seen at
specific wavelengths
W Five aberrations
of Seidel
a Spherical aberration
b Chromatic aberration
c Astigmatism
d Curvature of field
e Distortion
Chromatic aberration
When white light (light containing many
colours uniformly mixed so that the eye
does not sense any particular colour and
thus perceives the light as white) such as
sunlight is passed through a prism, a
rainbow spectrum can be observed. This
phenomenon occurs because the prism’s
index of refraction (and rate of dispersion)
varies depending on the wavelength (short
wavelengths are more strongly refracted
than long wavelengths). While most
visible in a prism, this phenomenon also
occurs in photographic lenses, and since it
occurs at different wavelengths is called
chromatic aberration. There are two types
of chromatic aberration: “axial chromatic
aberration,” where the focal point position
on the optical axis varies according to the
wavelength, and “chromatic difference of
magnification,” where the image
magnification in peripheral areas varies
according to the wavelength. In actual
photographs, axial chromatic aberration
appears as colour blur or flare, and
chromatic difference of magnification
appears as colour fringing (where edges
show colour along their borders).
Chromatic aberration in a photographic
lens is corrected by combining different
types of optical glass having different
refraction and dispersion characteristics.
Since the effect of chromatic aberration
increases at longer focal lengths, precise
chromatic aberration correction is
particularly important in super-telephoto
lenses for good image sharpness.
Although there is a limit to the degree of
correction possible with optical glass,
significant performance improvements
can be achieved using man-made crystal
such as fluorite or UD glass. Axial
chromatic aberration is also sometimes
referred to as “longitudinal chromatic
aberration” (since it occurs longitudinally
with respect to the optical axis), and
chromatic difference of magnification
Figure-18 Chromatic Aberration
can be referred to as “lateral chromatic
aberration” (since it occurs laterally with
respect to the optical axis).
Note: While chromatic aberration is most
noticeable when using colour film, it
affects black-and-white images as well,
appearing as a reduction in sharpness.
Achromat
A lens which corrects chromatic aberration for two wavelengths of light. When
referring to a photographic lens, the two
corrected wavelengths are in the blueviolet range and yellow range.
Apochromat
A lens which corrects chromatic aberration for three wavelengths of light,
with aberration reduced to a large
degree particularly in the secondary
spectrum. EF super-telephoto lenses are
examples of apochromatic lenses.
Five aberrations of Seidel
In 1856, a German named Seidel
determined through analysis the existence
of five lens aberrations which occur with
monochromatic (single wavelength) light.
These aberrations, described below, are
called the five aberrations of Seidel.
\\Bydproj1\DTP
a Spherical aberration
This aberration exists to some degree in
all lenses constructed entirely of spherical
elements. Spherical aberration causes
parallel light rays passing through the
edge of a lens to converge at a focal point
closer to the lens than light rays passing
through the center of the lens. (The
amount of focal point shift along the
optical axis is called longitudinal spherical
aberration.) The degree of spherical
aberration tends to be larger in largeaperture lenses. A point image affected by
spherical aberration is sharply formed by
light rays near the optical axis but is
affected by flare from the peripheral light
rays (this flare is also called halo, and its
radius is called lateral spherical
aberration). As a result, spherical
Figure-19 Spherical Aberration
VThis phenomenon occurs because the prism’s index of
refraction varies depending on the wavelength (colour).
Transverse chromatic aberration
(lateral chromatic aberration)
B
Y
Parallel light rays
R
VThis is the phenomenon where the focus is not
concentrated on one point on the light ray but rather is offset
to the front or back.
Occurrence of a halo–––The image becomes flare.
Optical axis
Off-axis object point
B Y R
Axial chromatic aberration
(longitudinal chromatic aberration)
198
M
Photo-2 The photographs are magnifications of the subject and surrounding area from part of a
test chart photographed with a 24mm x 36mm film frame and printed on quarter size
paper.
Almost ideal image formation
Photo-3 Axial chromatic aberration
Photo-4 Transverse chromatic aberration
Peripheral
a Example of spherical aberration
b-1 Example of inward coma
c Example of astigmatism
b-2 Example of outward coma
aberration affects the entire image area
from the center to the edges, and produces
a soft, low-contrast image which looks as
if covered with a thin veil. Correction of
spherical aberration in spherical lenses is
very difficult. Although commonly carried
out by combining two lenses –– one
convex and one concave –– based on light
rays with a certain height of incidence
(distance from the optical axis), there is a
limit to the degree of correction possible
using spherical lenses, so some aberration
always remains. This remaining
aberration can be largely eliminated by
stopping down the diaphragm to cut the
amount of peripheral light. With large
aperture lenses at full aperture, the only
effective way to thoroughly compensate
spherical aberration is to use an aspherical
lens element. → Aspherical lens
b Coma, comatic aberration
Coma, or comatic aberration, is a
phenomenon visible in the periphery of an
image produced by a lens which has been
corrected for spherical aberration, and
199
part magnified
the same point passing through the lens
center. Coma increases as the angle of the
principal ray increases, and causes a
decrease in contrast near the edges of the
image. A certain degree of improvement is
possible by stopping down the lens. Coma
can also cause blurred areas of an image
to flare, resulting in an unpleasing effect.
The elimination of both spherical
aberration and coma for a subject at a
certain shooting distance is called
aplanatism, and a lens corrected as such is
called an aplanat.
causes light rays entering the edge of the
lens at an angle to converge in the form of
a comet instead of the desired point, hence
the name. The comet shape is oriented
radially with the tail pointing either
toward or away from the center of the
image. The resulting blur near the edges
of the image is called comatic flare. Coma,
which can occur even in lenses which
correctly reproduce a point as a point on
the optical axis, is caused by a difference
in refraction between light rays from an
off-axis point passing through the edge of
the lens and the principal light ray from
c Astigmatism
With a lens corrected for spherical and
comatic aberration, a subject point on the
optical axis will be correctly reproduced as
a point in the image, but an off-axis
subject point will not appear as a point in
the image, but rather as an ellipse or line.
This type of aberration is called astigmatism, It is possible to observe this phenomenon near the edges of the image by
slightly shifting the lens focus to a position
Figure-21 Astigmatism
VThis is the phenomenon where there
is no point image
Figure-20 Comatic Aberration
VThis is the phenomenon where the diagonal light rays do not
focus on one point on the image surface.
Inward coma
This is the phenomenon where
there is a tail like that of a comet.
Outward coma
llel
ara
p
axis ays
Off- cil of r
pen
Optical axis
Principle ray
P2
P1
Lens
Sagittal image
Optical
axis
Po
Meridional image
P
where the subject point is sharply imaged
as a line oriented in a direction radiating
from the image center, and again to
another position.
d Curvature of Field
This is the phenomenon where, when
focusing on a flat surface, the image does
not become flat, but where the image is
formed in a bowed shape to the inside of
the bowl. Therefore, when focusing on the
center of the frame, the circumference is
blurred, and conversely, when focusing on
the circumference, the center is blurred.
This image bending is mainly changed
using the astigmatism correction method,
which creates an image between a sagittal
image and a meridional image, so the
more the astigmatism is corrected, the
smaller the image becomes. Because there
is almost no corrective effect from
stopping down the lens, various efforts are
made during designing, such as changing
the shape of the single lenses of the lens
configuration and selecting the aperture
position, but one of the requirements for
Figure-22 Curvature of field
correcting astigmatism and image bending
at the same time is Petzval’s condition
(1843). This condition is that the inverse of
the product of the index of refraction for
each of the single lenses of the lens
configuration and the focal distance added
with the number of single lenses used in
the lens configuration must produce a
sum of 0. This sum is called Petzval’s sum.
e Distortion
One of the conditions for an ideal lens is
that “the image of the subject and the
image formed by the lens are similar,” and
the deviation from this ideal where the
straight lines are bent is called distortion.
The extended shape in the diagonal view
angle direction (+) is called pincushion
distortion, and, conversely, the contracted
shape (—) is called barrel distortion. With
an ultra wide-angle lens, rarely do both of
these distortions exist together. Although
this seldom occurs in lenses where the
lens combination configuration is at the
aperture boundary, it occurs easily in
configuration lenses. Typical zoom lenses
Figure-23 Distortion
This is the phenomenon where a good image
focus surface is bent.
Barrel distortion (-)
VThis is an ideal lens with no image bending.
Pincushion distortion (+)
Lens
Subject surface
Subject
Lens
Focus surface
VOccurrence of image bending
Subject
Photo-5 Example of curvature of field
Photo-7 Example of distortion
Focusing on center of screen causes corners to go out of
focus.
+•Pincushion distortion
Photo-6 Example of curvature of field
Photo-8 Example of distortion
tend to exhibit barrel distortion at the
shortest focal lengths and pincushion
distortion at the longest focal lengths (the
distortion characteristics change slightly
during zooming), but in zoom lenses that
use an aspherical lens, the aspherical lens
is effective at removing distortion, so the
correction is good. This difference is
caused by the difference in refraction of
the principal rays passing through the
center of the lens, so it cannot be
improved no matter how much the
aperture is stopped down.
Meridional
A plane that includes a principal ray that
tries to capture a point outside the optical
axis and the optical axis is called a
meridional plane. The position linked to
the focal point by the light ray entering
through a lens of this shape is called the
meridional image plane. This is the image
plane where the image of concentric
circles in the frame are at the best. If the
spherical surface of the lens is compared
to a portion of the earth’s curvature and if
the optical axis is compared to the earth’s
axis, the meridional plane would be where
the earth’s meridian is, which is why this
name is used. The curve that expresses the
characteristics of this image plane using a
MTF characteristics graph, etc., is often
abbreviated as “M.”
Sagittal
The plane that is perpendicular to the
meridional plane is called the sagittal
plane, and this is the image plane where
the radial image is at its best. The word
comes from the Greek word for arrow.
The name comes from the shape of the
focal point, which spreads radially. The
position linked to the focal point of a light
ray that passes through a sagittal plane
shape and into a lens is called the sagittal
image plane, and when the characteristics
of this image plane are expressed using a
MTF characteristics graph, etc., it is often
abbreviated using the initial “S.”
How to Read Distortion Graphs
A simple way of reading the aberration
graphs that accompany test report
articles in camera magazines.
V Spherical Distortion
Characteristics Graph (Graph1)
The vertical axis of the graph shows the
height of entry above the axis entering the
lens system (distance above the diagonal
Focusing on corners of screen causes center to go out of
focus.
-•Barrel distortion
200
from the center of the frame), and the
horizontal axis shows the image point
offset captured by the film surface shape.
The unit is mm. The horizontal axis
symbols are “—“ (minus), which shows the
subject’s side direction, and “+” (plus),
which shows the film’s side direction. The
ideal lens characteristic is for the horizontal
axis zero point to form a straight line with
the entry height. The difference between
this ideal and the actual lens is shown as a
curve. Spherical distortion correction is
generally said to be good if there is a core
in the image and the focal point moves
little when the lens is stopped down, in
other words, there is slightly insufficient
correction in the middle area while at the
maximum entry height there is perfect
correction where it returns nearly to zero.
lens system, and the horizontal axis is
percent (%) distortion. The curve indicates
the difference between the ideal image
and the actual image formed at the focal
plane. A minus sign indicates negative, or
barrel, distortion where the length of the
diagonal of the actual image is shorter
than the diagonal of the ideal image. A
plus sign indicates positive, or pincushion,
distortion. An ideal lens would exhibit
±0% distortion at any image height.
Distortion curves for zoom lenses
generally show barrel distortion at wideangle positions and pincushion distortion
at telephoto positions.
modern lenses are often designed with
consideration given to achieving a
pleasing blur effect (image characteristics
outside the image formation plane) by
using computer simulation techniques to
analyze lens performance at the design
stage. As mentioned in the various
aberration descriptions, the effects of some
aberrations can be minimised by stopping
down the lens, while others cannot. The
relationships between aperture and
aberrations are shown in Table 2.
Lens performance evaluation
Resolving power/resolution
The resolution of a lens indicates the
capacity of reproduction of a subject point
of the lens. The resolution of the final
photograph depends on three factors: the
resolution of the lens, the resolution of the
film or image sensor, and the resolution of
the printer or printing paper. Resolution is
evaluated by photographing, at a specified
Figure-25 Astigmatism
Distortion Curve
Curve (Graph2) (Graph3)
[mm]
20
Figure-24 Spherical Distortion
Characteristics Graph (Graph 1)
[mm]
S
20
M
[mm]
20
10
10
Figure-26 Resolution Measurement Charts
Resolution chart (koana)
-0.6
0
+0.6 [mm]
-5
0
+5 [%]
10
[mm]
V Astigmatism curve (Graph 2)
The graph’s vertical axis is the axial height
of incidence (distance from the image
center) of the ray entering the lens system,
and the horizontal axis is the amount of
shift of the image point formed in the
focal plane. Units and signs are the same
as in the spherical aberration curve. The
curve for an ideal lens would be a straight
line at the horizontal axis’ zero point with
respect to the height of incidence. The
difference between the ideal lens and
actual lens is indicated by two curved lines
in the S direction (sagittal/radial direction)
and M direction (meridional/concentric
circle direction). If the difference between
S and M (astigmatic difference) is large, a
point will not be formed as a point and
the image will smear. Moreover, the blur
image in front of and behind the image
formation plane will be unnatural.
V Distortion curve (Graph 3)
The graph’s vertical axis is the axial height
of incidence (distance from the image
center; unit: mm) of the ray entering the
201
Resolution chart (JIS)
B
D
C
B
+0.2
D
0
C
0
-0.2
How to minimise the effects of
aberrations
Modern lenses are designed using largescale computers to perform mind-boggling
calculations and high-level simulations to
minimise all types of aberration and
achieve superior image formation
performance. Even with this technology,
however, it is impossible to completely
remove all aberrations, meaning that all
lenses on the market still have at least a
small amount of aberration remaining.
This aberration is called residual
aberration. The type of residual aberration
in a lens generally determines the lens’
imaging characteristics such as its
sharpness and blur effect. Because of this,
Siemens star
Projection-use resolution chart
Howllet chart
Table-2 Relationship between aperture and aberration
Areas affected on the screen
Improvement by smaller aperture
Center and edges
Slight effect
Edges
No effect
Spherical aberration
Center and edges
Effect present
Comatic aberration
Edges
Effect present
Astigmatism
Edges
Slight effect
Curvature of field
Edges
Slight effect
Distortion
Edges
No effect
Cause of drop in image quality
Axial colour aberration
Magnification colour aberration
Ghosting/flaring
Drop in peripheral illumination
Center and edges
No effect
Edges
Effect present
magnification, a chart containing groups
of black and white stripes that gradually
decrease in narrowness, then using a
microscope to observe the negative image
at a magnification of 50x.
It is common to hear resolution expressed
as a numerical value such as 50 lines or
100 lines. This value indicates the number
of lines per millimeter of the smallest
black and white line pattern which can be
clearly recorded on the film. To test the
resolution of a lens alone, a method is
used in which a fine resolution chart is
positioned in the location corresponding to
the focal plane and projected through the
test lens onto a screen. The numerical
value used for expressing resolving power
is only an indication of the degree of
resolution possible, and does not indicate
resolution clarity or contrast.
Contrast
The degree of distinction between areas of
different brightness levels in a photograph,
i.e., the difference in brightness between
light and dark areas. For example, when
the reproduction ratio between white and
black is clear, contrast is said to be high,
Figure-27 Contrast Concept Diagram
Light from
subject
(incoming)
Image
forming
lights (exiting)
Light from
subject
(incoming)
Figure-27-A
Image
forming
lights (exiting)
Figure-27-C
Figure-27-D
Figure-27-B
Contrast Reproduction Image
Chart
Image formed by
Image formed by
large-aperture aspherical lens large-aperture spherical lens
High contrast
Low contrast
Figure-27-E MTF Measurement-Use Slit Chart
MTF (modulation transfer
function)
Modulation transfer function is a lens
performance evaluation method used to
determine the contrast reproduction ratio,
or sharpness, of a lens. When evaluating
the electrical characteristics of audio
equipment, one important measure of
performance is frequency response. In this
case, where the source sound is recorded
through a microphone and then played
back through speakers, frequency
response indicates the fidelity of the
reproduced sound with respect to the
source sound. If the reproduced sound is
very close to the source sound, the
equipment is classified as “hi-fi,” or “high
fidelity.” By thinking of the optical system
of a lens as a “system for transmitting
optical signals” in the same way as an
audio system transmits electrical signals, it
is possible to find out how accurately
optical signals are transmitted as long as
the frequency response of the optical
system can be measured. In an optical
system, the equivalent of frequency is
“spatial frequency,” which indicates how
many patterns, or cycles, of a certain sine
density are present in a 1 mm width.
Accordingly, the unit of spatial frequency
is lines per mm. Figure-27-A shows the
MTF characteristics of an ideal “hi-fi” lens
for a certain spatial frequency, with the
output equal to the input. A lens of this
type is said to provide a contrast of 1:1.
However, since actual lenses contain
residual aberration, actual contrast ratios
are always less than 1:1. As the spatial
frequency increases (i.e., as the black-andwhite sine wave pattern becomes finer, or
more dense), the contrast decreases as
shown in Figure-27-D until finally
becoming gray with no distinction
between black and white (no contrast, 1:0)
at the spatial frequency limit. Illustrating
this phenomenon in graph form with
spatial frequency as the horizontal axis
and contrast as the vertical axis results in
the curve shown in Graph-4. In other
words, the graph makes it possible to
check resolution and contrast reproducibility (i,e., the degree of modulation) in
a continuous manner. However, since it
only shows the characteristics for one
point in the image area, it is necessary to
use data for several points in order to
determine the MTF characteristics of the
overall image. Because of this, for the EF
lens MTF characteristics presented in this
book, two typical spatial frequencies (10
lines/mm and 30 lines/mm) are selected
and sophisticated computer simulation
techniques are used to determine the MTF
characteristics of the entire image area,
graphed with the horizontal axis
corresponding to the distance from the
center of the image along the diagonal
line, and the vertical axis corresponding to
contrast.
How to read the MTF graphs
The MTF graphs shown for the lenses in
this book place image height (with the
image center having an image height of 0)
on the horizontal axis and contrast on the
vertical axis. MTF characteristics are
provided for spatial frequencies of 10
lines/mm and 30 lines/mm. The test
chart’s spatial frequency, lens aperture
value and direction in the image area are
as shown in the following table.
Basic information on the performance of a
lens can be extracted from the MTF chart
as follows: The closer the 10-line/mm
curve is to 1, the better the contrast and
separation ability of the lens, and the
closer the 30-line/mm curve is to 1, the
better the resolving power and sharpness
of the lens. Additionally, the closer the
characteristics of M and S are, the more
natural the background blur becomes.
Although a good balance between these
characteristics is important, it can
generally be assumed that a lens will
provide excellent image quality if the 10line/mm curve is greater than 0.8, and that
satisfactory image quality can be obtained
if the l0-line/mm curve is greater than 0.6.
Looking at the MTF characteristics of EF
super-telephoto L-series lenses with this
frame of reference, it is obvious from just
the data that these lenses possess
extremely high-performance imaging
characteristics.
Graph-4 MTF Characteristics for A Single
Image Point
1
Contrast
Density
difference
and when unclear, contrast is said to be
low. In general, lenses producing high
quality images have both high resolution
and high contrast.
A
C
B
0.5
0
0
10
30
50
Spatial frequency(line/mm)
202
CCI (colour contribution index)
Colour reproduction in a colour
photograph depends on three factors: the
colour characteristics of the film or digital
imaging system, the colour temperature of
the light source illuminating the subject,
and the light transmission characteristics of
the lens. The colour contribution index, or
CCI, is an index indicating “the amount of
colour variation caused by filtering effect
differences between lenses” when using a
standard film and light source, and is
expressed by three numbers in the form
0/5/4. These three numbers are relative
values expressed as logarithms of lens
transmittance at the blue-violet/green/red
wavelengths corresponding to the three
light sensitive emulsion layers of colour
film, with larger numbers representing
higher transmittance. However, since
photographic lenses absorb most
ultraviolet wavelengths, the blue-violet
transmittance value is usually zero, so
colour balance is judged by comparing the
green and red values to ISO-specified
reference lens values. The ISO reference
lens light transmission characteristics were
set according to a method proposed by
Japan which involved taking the average
transmittance values of 57 standard lenses
A:Resolving power and contrast are both good
B:Contrast is good and resolving power is bad
Graph-6 ISO Tolerance Range Graphed on
CCI Coordinates
C:Resolving power is good and contrast is bad
Yellow
Table-3
Spatial frequency
F8
Maximum aperture
S
M
S
M
10 lines/mm
30 lines/mm
S
Graph-5 MTF Characteristics
Green
1.0
0.9
1.0
0.8
0.6
0.4
0.3
0.2
0.1
0
5
10
15
20
Colour balance
The colour reproduction fidelity of a photo
taken through a lens compared to the
original subject. Colour balance in all EF
lenses is based on ISO recommended
reference values and maintained within a
strict tolerance range narrower than ISO’s
CCI allowable value range.→ CCI
Graph-7 Image Plane Illuminance Ratio
Showing the Peripheral Illumination
Characteristics
100
[%]
f/8
f/2.8
50
0
0
10
20
Image height [mm]
Optical vignetting
Light rays entering the lens from the
edges of the picture area are partially
blocked by the lens frames in front of
and behind the diaphragm, preventing
all the rays from passing through the
effective aperture (diaphragm diameter)
and causing light fall-off in the
peripheral areas of the image. This type
of vignetting can be eliminated by
stopping down the lens.
Figure-28 Vignetting
1.0
Blue Magenta Origin
0.5
203
0/0/0
Red
B
Cyan
1.0
0.7
0
R
G
indicates the brightness at the optical
axis position, i.e., at the center of the
image. The brightness (image surface
illuminance) at the edge of the image is
called peripheral illumination and is
expressed as a percent (%) of the
amount of illumination at the image
center. Peripheral illumination is
affected by lens vignetting and the cos4
(cosine 4) law and is inevitably lower
than the center of the image.→
Vignetting, Cos4 law
comprising five models from representative
lens manufacturers including Canon. The
resulting recommended reference value of
0/5/4 is used by film manufacturers as a
reference when designing the colour
production characteristics of colour films. In
other words, if the light transmission
characteristics of a lens do not match the
ISO reference values, the colour
reproduction characteristics of a colour film
cannot be obtained as intended by the
manufacturer.
Peripheral illumination
The brightness of a lens is determined
by the F number, but this value only
y
ht ra
l lig
Front frame Rear frame
hera
Diaphragm
Perip
Central light ray
Cosine law
The cosine law, also called the cosine law,
states that light fall-off in peripheral areas
of the image increases as the angle of
view increases, even if the lens is
completely free of vignetting. The peripheral image is formed by groups of light
rays entering the lens at a certain angle
with respect to the optical axis, and the
amount of light fall-off is proportional to
the cosine of that angle raised to the
Graph-8 Peripheral Light Reduction According to
Cosine Law
(%)
Illumination ratio
100
a'
Lens
P
p'
w
50
a
Uniform brightness
0
0 10 20 30 40 50 60 70
Incident angle
fourth power. As this is a law of physics, it
cannot be avoided. However, with wideangle lenses having a large angle of view,
decreases in peripheral illumination can
be prevented by increasing the lens’
aperture efficiency (ratio of the area of the
on-axis entrance pupil to the area of the
off-axis entrance pupil).
Hard vignetting
A phenomenon where light entering the
lens is partially blocked by an
obstruction such as the end of a lens
hood or the frame of a filter, causing
the corners of the image to darken or
the overall image to lighten. Shading is
the general term used for the case
where the image is degraded by some
type of obstacle that blocks light rays
which should actually reach the image.
Flare
Light reflected from lens surfaces, the
inside of the lens barrel and the inner
walls of the camera’s mirror box can reach
the film or image sensor and fog part or
all of the image area, degrading image
sharpness. These harmful reflections are
called flare. Although flare can be reduced
to a large extent by coating the lens
surfaces and using anti-reflection
measures in the lens barrel and camera,
flare cannot be completely eliminated for
all subject conditions. It is therefore
Figure-29 Flare and Ghosting
Correct
Image
Correct
Image
Lens
Ghost
Lens
Flare
desirable to use an appropriate lens hood
whenever possible. The term “flare” is also
used when referring to the effects of
blurring and halo caused by spherical and
comatic aberration.
Ghost image
A type of flare occurring when the sun or
other strong light source is included in the
scene and a complex series of reflections
among the lens surfaces causes a clearly
defined reflection to appear in the image
in a position symmetrically opposite the
light source. This phenomenon is
differentiated from flare by the term
“ghost” due to its ghost-like appearance.
Ghost images caused by surface reflections
in front of the aperture have the same
shape as the aperture, while a ghost image
caused by reflections behind the aperture
appears as an out-of-focus area of light
fogging. Since ghost images can also be
caused by strong light sources outside the
picture area, use of a hood or other
shading device is recommended for
blocking undesired light. Whether or not
ghosting will actually occur when the
picture is taken can be verified beforehand
by looking through the viewfinder and
using the camera’s depth-of-field check
function to close down the lens to the
actual aperture to be used during
exposure.
Coating
When light enters and exits an uncoated
lens, approximately 5% of the light is
reflected back at each lens-air boundary
due to the difference in index of refraction.
This not only reduces the amount of light
passing through the lens but can also lead
to repeating reflections which can cause
unwanted flare or ghost images. To
prevent this reflection, lenses are
processed with a special coating. Basically
this is carried out using vacuum vapor
deposition to coat the lens with a thin film
having a thickness 1/4 the wavelength of
the light to be affected, with the film made
of a substance (such as magnesium
fluoride) which has an index of refraction
of √n, where n is the index of refraction of
the lens glass. Instead of a single coating
affecting only a single wavelength,
however, EF lenses feature a superior
multi-layer coating (multiple layers of
vapor deposited film reducing the
reflection rate to 0.2~0.3%) which
effectively prevents reflections of all
wavelengths in the visible light range.
Lens coating is carried out not only to
prevent reflections, however. By coating
the various lens elements with appropriate
substances having different properties,
coating plays an important role in
providing the overall lens system with
optimum colour balance characteristics.
Optical Glass
Optical Glass
Optical glass is specially made for use in
precision optical products such as
photographic lenses, video lenses,
telescopes and microscopes. In contrast to
general-purpose glass, optical glass is
provided with fixed, precise refraction and
dispersion characteristics (precision to six
decimal points) and subjected to strict
requirements regarding transparency and
lack of defects such as striae, warps and
bubbles. Types of optical glass are
classified according to their composition
and optical constant (Abbe number), and
more than 250 types are in existence
today. For high-performance lenses,
different types of optical glass are
optimally combined. Glass with an Abbe
number of 50 or less is called flint glass
(F), and glass with an Abbe number of 55
or more is called crown glass (K). Each
type of glass is further classified in other
ways such as specific gravity, and a
corresponding serial name is assigned to
each type.
Abbe number
A numerical value indicating the
dispersion of optical glass, using the Greek
symbol ν. Also called the optical constant.
The Abbe number is determined by the
following formula using the index of
refraction for three Fraunhofer’s lines: F
(blue), d (yellow) and c (red).
Abbe number = νd = nd — 1/nF — nc
Fraunhofer’s lines
Absorption lines discovered in 1814 by a
German physicist named Fraunhofer
(1787~1826), comprising the absorption
spectrum present in the continuous
spectrum of light emitted from the sun
created by the effect of gases in the sun’s
and earth’s atmospheres. Since each line is
located at a fixed wavelength, the lines are
used for reference in regard to the colour
(wavelength) characteristics of optical
glass. The index of refraction of optical
glass is measured based on nine
204
wavelengths selected from among
Fraunhofer’s lines (see Table 4). In lens
design, calculations for correcting
chromatic aberrations are also based on
these wavelengths.
Table-4 Light Wavelengths and Spectrum
Lines
Spectrum
line code
i
h
g
F
Wavelength (mm)
365,0
404,7
435,8
486,1
Colour
Ultra-violet
Violet
Blue-violet
Blue
Spectrum
line code
e
d
c
Wavelength (mm)
546,1
587,6
656,3
Colour
Green
Yellow
Red
r
manufacturer to develop lead free glass,
and is in the process of phasing out glass
which contains lead from its lens lineup.
Lead free glass uses titanium, which,
unlike lead, poses no problems for the
environment or humans, but still delivers
optical
characteristics
equal
to
conventional leaded glass.
Lens shapes and lens
construction fundamentals
Lens shapes
t
706,5
1014
Red
Infrared
Figure-30 Lens Shapes
Plane-convex lens
Biconvex lenses
Convex meniscus lens
-6
Note: 1 nm = 10 mm
Fluorite
Fluorite has extremely low indexes of
refraction and dispersion compared to
optical glass and features special partial
dispersion characteristics (extraordinary
partial dispersion), enabling virtually ideal
correction of chromatic aberrations when
combined with optical glass. This fact has
long been known, and in 1880 natural
fluorite was already in practical use in the
apochromatic objective lenses of microscopes. However, since natural fluorite
exists only in small pieces, it cannot be
used practically in photographic lenses. In
answer to this problem, Canon in 1968
succeeded in establishing production
technology for manufacturing large
artificial crystals, thus opening the door for
fluorite use in photographic lenses.
UD lens
A lens made of special optical glass
possessing optical characteristics similar to
fluorite. UD lens elements are especially
effective in correcting chromatic aberrations in super-telephoto lenses. Two UD
lens elements are characteristically
equivalent to one fluorite element. “UD”
stands for “ultra-low dispersion.”
Lead-Free Glass
This is a type of optical glass which
contains no lead, to relieve the burden on
the environment. Lead is used in many
types of optical glass because it raises the
refractive power of glass. While the lead
cannot leak out of the glass it is contained
in, it does nevertheless pose a threat to the
environment when it escapes in the form
of waste produced when grinding and
polishing the glass. With the goal of
eliminating lead from the manufacturing
process, Canon worked with a glass
205
Plane-concave lenses Biconcave lens
Concave meniscus lens
Fresnel lens
A type of converging lens, formed by
finely dividing the convex surface of a flat
convex lens into many concentric circleshaped ring lenses and combining them to
extremely reduce the thickness of the lens
while retaining its function as convex lens.
In an SLR, to efficiently direct peripheral
diffused light to the eyepiece, the side
opposite the matte surface of the focusing
screen is formed as a fresnel lens with a
0.05 mm pitch Fresnel lenses are also
commonly used in flash units, indicated
by the concentric circular lines visible on
the white diffusion screen covering the
flash tube. The projection lens used to
project light from a lighthouse is an
example of a giant fresnel lens.
special lens element with a surface curved
with the ideal shape to correct these
aberrations, i.e., a lens having a free-curved
surface which is not spherical, is called an
aspherical lens. The theory and usefulness
of aspherical lenses. have been known
since the early days of lens making, but
due to the extreme difficulty of actually
processing and accurately measuring
aspherical surfaces, practical aspherical
lens manufacturing methods were not
realised until fairly recently. The first SLR
photographic lens to incorporate a large
diameter aspherical lens was Canon’s
FD 55mm f/1.2AL released in March 1971.
Due to revolutionary advances in
production technology since that time,
Canon’s current EF lens group makes
abundant use of various aspherical lens
types such as ground and polished glass
aspherical lens elements, ultra-precision
glass molded (GMo) aspherical lens
elements, composite aspherical lens
elements and replica aspherical lens
elements.
Air lens
The air spaces between the glass lens
elements making up a photographic lens
can be thought of as lenses made of glass
having the same index of refraction as air
(1.0). An air space designed from the
beginning with this concept in mind is
called an air lens. Since the refraction of
an air lens is opposite that of a glass lens,
a convex shape acts as a concave lens and
a concave shape acts as a convex lens.
This principle was first propounded in
1898 by a man named Emil von Hoegh
working for the German company Goerz.
Figure-32 Air Lens Concept Diagram
ML
H
M
H
Figure-31 Fresnel Lens
↑
L (air space)
Aspherical lens
Photographic lenses are generally
constructed of several single lens elements,
all of which, unless otherwise specified,
have spherical surfaces. Because all
surfaces are spherical, it becomes
especially difficult to correct spherical
aberration in large-aperture lenses and
distortion in super-wide-angle lenses. A
Actual photographic lenses
When looking at the enlarged image of an
object through a magnifying glass, it is
common for the edges of the image to be
distorted or discoloured even if the center
is clear. As this indicates, a single-element
lens suffers from many types of aberrations and cannot reproduce an image
which is clearly defined from corner to
corner. Because of this, photographic
lenses are constructed of several lens
elements having different shapes and
characteristics in order to obtain a sharp
image over the entire picture area. The
basic construction of a lens is listed in the
specifications section of brochures and
instruction manual in terms of elements
and groups. Figure 33 shows an example
of the EF 85mm f/1.2L II USM, constructed
of 8 elements in 7 groups.
Figure-33 EF 85mm f/1.2L@USM Lens
Construction
1 2
1 2
3
3
4
4
5 6
5
7 8 (Elements)
6 7 (Groups)
Fundamentals of lens
construction
There are five basic constructions used for
general-purpose single focal length lenses.
a The single type is the simplest ——
comprised of a single element or a doublet
made of two conjoined elements. b and
c are of the double type, comprised of
two independent elements. d is a triplet
type, comprised of three independent lens
elements in a convex-concave-convex
sequence. e is a symmetrical type,
consisting of two groups of one or more
lenses of the same shape and
configuration symmetrically oriented
around the diaphragm.
Figure-34 Fundamental Lens Groupings
Group 1
Group 2
Group 3
Group 4
Group 5
Typical photographic lens types
V Single focal length lenses
a Symmetrical type
In this type of lens, the lens group behind
the diaphragm has nearly the same
configuration and shape as the lens group
in front of the diaphragm. Symmetrical
lenses are further classified into various
types such as the Gauss type, triplet type,
Tessar type, Topcon type and orthometer
type. Of these, the Gauss type and its
derivations is the most typical
configuration used today because its
symmetrical design allows well balanced
correction of all type of aberrations, and a
comparatively long back focus can be
achieved. The Canon 50mm f/1.8 released
back in 1951 succeeded in eliminating the
comatic aberration which was the sole
weak point of Gauss type lenses of that
day, and thus became famous as a
historical landmark lens due to the
remarkable improvement in performance
it afforded. Canon still uses a Gauss type
construction in current lenses such as the
EF 50mm f/1.4 USM, EF 50mm f/1.8 II
and EF 85mm f/1.2L II USM. The Tessar
and
triplet
type
symmetrical
configurations are commonly used today
in compact cameras equipped with single
focal length lenses.
Figure-35 Typical Photographic Lens Types
Triplet type
Tessar type
the value of the distance from the apex of
the frontmost lens element to the focal
plane divided by the focal length. For
telephoto lenses, this value is less than one.
For reference, the telephoto ratio of the
EF 300mm f/2.8L IS USM is 0.94, and that
of the EF 600mm f/4L IS USM is 0.81.
Figure-36 Telephoto Type
c Retrofocus type
Conventionally designed wide-angle lenses
have such a short back focus that they
cannot be used in SLR cameras because
they would obstruct the up/down
swinging movement of the main mirror.
Because of this, wide-angle lenses for SLRs
have a construction opposite that of
telephoto lenses, with a negative lens
assembly placed in front of the main lens
assembly. This moves the second principal
point behind the lens (between the
rearmost lens element and the film plane)
and creates a lens having a back focus
which is longer than the focal length. This
type of lens is generally called a retrofocus
lens from the name of a product marketed
by Angenieux Co. of France. In optical
terms, this type of lens is classified as an
inverted telephoto type lens.
Figure-37 Inverted Telephoto Types
(Retrofocus)
Gauss type
Topogon type
b Telephoto type (teletype)
With general photographic lenses, the
overall length of a lens (the distance from
the apex of the frontmost lens element to
the focal plane) is longer than its focal
length. This is not usually the case with
lenses of particularly long focal length,
however, since using a normal lens
construction would result in a very large,
unwieldy lens. To keep the size of such a
lens manageable while still providing a
long focal length, a concave (negative) lens
assembly is placed behind the main
convex (positive) lens assembly, resulting
in a lens which is shorter than its focal
length. Lenses of this type are called
telephoto lenses. In a telephoto lens, the
second principal point is located in front of
the frontmost lens element.
V Telephoto ratio
The ratio between the overall length of a
telephoto lens and its focal length is called
the telephoto ratio. Put another way, it is
Zoom lenses
d 4-group zoom type
An orthodox zoom lens configuration
which clearly divides the functions of the
lens into four groups (focusing group,
magnification variation group, correction
group and image formation group). Two
groups –– the magnification variation
group and correction group –– move
during zooming. Since a high-magnification zoom ratio can be easily
obtained with this type of construction, it
is commonly used for movie camera
lenses and SLR telephoto zoom lenses.
However, due to problems incurred when
designing compact zoom lenses, its use is
becoming less common in modern nontelephoto zoom lenses.
e Short zoom type
Explanation → P.175
206
f Multi-group zoom type
Explanation → P.175
Figure-38 Shooting Distance, Subject Distance and Image Distance
Front principal point Rear principal point
h
h'
Subject
Focusing and lens movement
Focal plane
Focusing and lens movement
techniques
Methods of lens movement for focusing
can be broadly classified into the five
types described below.
a Overall linear extension
The entire lens optical system moves
straight backward and forward when
focusing is carried out. This is the simplest
type of focusing used in mainly in wideangle through standard single focal length
lenses, Such as the EF 15mm f/2.8
Fisheye, lense, the EF 50mm f/1.4 USM,
the TS-E 90mm f/2.8, and other EF lenses.
b Front group linear extension
The rear group remains fixed and only the
front group moves straight backward and
forward during focusing. Examples of
front group linear extension lenses are the
EF 50mm f/2.5 Compact Macro,
MP-E 65mm f/2.8 Macro Photo and
EF 85mm f/1.2L II USM.
c Front group rotational extension
The lens barrel section holding the front
lens group rotates to move the front group
backward and forward during focusing.
This type of focusing is used only in zoom
lenses and is not found in single focal
length lenses. Representative examples of
lenses using this method are the EF 2890mm f/4-5.6 III, EF 75-300mm f/4-5.6 IS
USM and EF 90-300mm f/4.5-5.6 USM
and other EF lenses.
d Inner focusing
Focusing is performed by moving one or
more lens groups positioned between the
front lens group and the diaphragm.
→ P.176
e Rear focusing
Focusing is performed by moving one or
more lens groups positioned behind the
diaphragm. → P.177
Floating system
This system varies the interval between
certain lens elements in accordance with
the extension amount in order to compensate for aberration fluctuation caused
by camera distance. This method is also
referred to as a close-distance aberration
compensation mechanism. → P.177
207
Focal length
Principal
point
interval
Extension
amount
Focal length
Subject distance
Image distance
Working distance
Machanical distance
Shooting distance
Shooting distance/subject
distance/image distance
Camera distance
The distance from the focal plane to the
subject. The position of the focal plane is
indicated on the top of most cameras by a
“ ” symbol.
proportional value indicating the size of
the image compared to the actual subject.
(For example, a magnification of 1:4 is
expressed as 0.25x.)
Figure-39 Relationship Between the Focal
Length, Extension Amount (Overall
Extension) and Magnification
y
Subject distance
The distance from the lens’ front
principal point to the subject.
y'
f
f
r
e
R
Image distance
The distance from the lens’ rear principal
point to the focal plane when the lens is
focused on a subject at a certain distance.
Extension amount
With a lens which moves the entire
optical system backward and forward
during focusing, the amount of lens
movement necessary to focus a subject
at a limited distance from the infinity
focus position.
Mechanical distance
The distance from the front edge of the
lens barrel to the focal plane.
Working distance
The distance from the front edge of the
lens barrel to the subject. An important
factor especially when shooting closeups and enlargements.
Image magnification
The ratio (length ratio) between the actual
subject size and the size of the image
reproduced on film. A macro lens with a
magnification indication of 1:1 can
reproduce an image on film the same size
as the original subject (actual size).
Magnification is generally expressed as a
R
M
(r f)2 e
r
f(M 1)2
e
M
y' r'
y
f
f
r
e
R
y
y'
M
Focal length
Extension amount
Principal point interval
Shooting distance
Subject size
Subject size on the film plane
Magnification
Polarized light and
polarizing filters
Polarized light
Since light is a type of electromagnetic
wave, it can be thought of as uniformly
vibrating in all directions in a plane
perpendicular to the direction of
propagation. This type of light is called
natural light (or natural polarized light). If
the direction of vibration of natural light
becomes polarized for some reason, that
light is called polarized light. When
Figure-40 Naturally Polarized Electromagnetic
Wave
Partially polarized light
Naturally
polarized light
(natural light)
Light
propagation
direction
natural light is reflected from the surface
of glass or water, for example, the
reflected light vibrates in one direction
only and is completely polarized. Also, on
a sunny day the light from the area of the
sky at a 90° angle from the sun becomes
polarized due to the effect of air molecules
and particles in the atmosphere. The halfmirrors used in autofocus SLR cameras
also cause light polarization.
Linear polarizing filter
A filter which only passes light vibrating
in a certain direction.
Since the
vibrational locus of the light allowed to
pass through the filter is linear in nature,
the filter is called a linear polarizing filter.
This type of filter eliminate reflections
from glass and water the same way as a
circular polarizing filter, but it cannot be
used effectively with most auto exposure
and autofous cameras as it will cause
exposure errors in AE cameras equipped
with TTL metering systems using halfmirrors, and will cause focusing errors in
AF cameras incorporating AF rangefinding systems using half-mirrors.
Circular polarizing filter
A circular polarizing filter is functionally
the same as a linear polarizing filter as it
only passes light vibrating in a certain
direction. However, the light passing
through a circular polarizing filter differs
from light passing through a linear
polarizing filter in that the vibrational
locus rotates in a spiral pattern as it
propagates. Thus, the effect of the filter
does not interfere with the effect of halfmirrors, allowing normal operation of
TTL-AE and AF functions. When using a
polarizing filter with an EOS camera, be
sure to always use a circular polarizing
filter. The effectiveness of a circular
polarizing filter in eliminating reflected
light is the same as that of a linear
polarizing filter.
Digital Terminology
Image sensor
A semiconductor element which converts
image data into an electric signal, playing
the role of the film in a regular film
camera. Also known as an imager. The
two most common image elements used
in digital cameras are CCD (ChargeCoupled
Devices)
and
CMOS
(Complementary Metal-Oxide Semiconductors). Both are area sensors
containing a large number of receptors
(pixels) on a flat surface which convert
variations in light into electric signals. The
higher the number of receptors, the more
accurate the image reproduction is. Since
these receptors are only sensitive to
brightness and not colour, RGB or CMYG
colour filters are placed before them in
order to capture both brightness and
colour data at the same time.
Low-pass filter
With general image elements used in
digital cameras, RGB or CMYG colour
information is collected for each receptor
arranged on the surface. This means that
when light with a high spatial frequency
hits a single pixel, false colours, moiré, and
other colours which do not exist in the
subject appear in the image. In order to
reduce the occurrence of these types of
false colours, the light must made to enter
many different receptors, and in order to
do that, the receptors used are low-pass
filters. Low-pass filters use liquid crystal
and other crystal structures which are
characterised by double refraction (a
phenomenon where two streams of
refracted light are created), placed before
the image elements. By double-refracting
light with a high spatial frequency using
low-pass filters, it becomes possible to
receive light using multiple elements.
The human eye and
viewfinder diopter
Eyesight, visual acuity
The ability of the eye to distinguish details
of an object’s shape. Expressed as a
numerical value which indicates the
inverse of the minimum visual angle at
which the eye can clearly distinguish two
points or lines, i.e. the resolution of the eye
in reference to a resolution of 1’. (Ratio
with a resolution of 1’ assumed as 1.)
Eye accommodation
Figure-41 Human Eye Construction
Posterior chamber
Limbal zone
ry
lia
Ci ody
b
Anterior
chamber
Cornea
Iris
Conjunctiva
Canal of Schlemm
Ciliary muscle
Crystal lens
Ciliary process
Retrolental space
Optical axis
Zonule fibers
Ciliary epithelium
Eye central axis
Glass
Retina
Sclera
Choroid
Optic nerve
Dis
c
Fovea
centralis
The ability of the eye to vary its refractive
power in order to form an image of an
object on the retina. The state in which the
eye is at its minimum refractive power is
called the accommodation rest state.
Normal vision, emmetropia
The eye condition in which the image
of an infinitely distant point is formed
on the retina when the eye is in the
accommodation rest state.
Far-sightedness
The eye condition in which the image
of an infinitely distant point is formed
to the rear of the retina when the eye is
in the accommodation rest state.
Near-sightedness, myopia
The eye condition in which the image
of an infinitely distant point is formed
in front of the retina when the eye is in
the accommodation rest state.
Astigmatism
The eye condition in which astigmatism
exists on the eye’s visual axis.
Presbyopia
The eye condition in which the ability
of the eye to focus decreases as a person
becomes older. In camera terms, this is
similar to having a fixed focal point
with a shallow depth of field.
Least distance of distinct vision
The closest distance at which an eye
having normal vision can observe an
object without straining. This distance is
normally assumed to be 25 cm/0.8 ft.
Diopter
The degree to which the light ray
bundles leaving the viewfinder converge
or disperse. The standard diopter of all
EOS cameras is set at —1 dpt. This
setting is designed to allow the finder
image to appear to be seen from a
distance of 1 m. Thus, if a person
cannot see the viewfinder image clearly,
the person should attach to the camera’s
eyepiece a dioptric adjustment lens
having a power which, when added to
the viewfinder’s standard diopter,
makes it possible to easily see an object
at one meter. The numerical values
printed on EOS dioptric adjustment
lenses indicate the total diopter
obtained when the dioptric adjustment
lens is attached to the camera.
Yellow
spot
208
MTF Characteristics
How to read the MTF Characteristics
An MTF characteristic
of 0.8 or more at 10
lines/mm indicates
a superior lens.
Curve showing contrast
at maximum aperture
1
0.9
0.8
0.7
0.6
0.5
An MTF characteristic
of 0.6 or more at 10
lines/mm indicates
a satisfactory image.
Curve showing resolution
at maximum aperture
0.4
0.3
0.2
0.1
0
0
5
Spatial
frequency
10
15
Maximum aperture
S
M
20
(mm) Distance from the
center of the frame
f/8
S
M
10 lines/mm
30 lines/mm
The more the S and M curves are in line, the more natural the
blurred image becomes.
Resolving power and contrast are
both good
Contrast is good and resolving
power is bad
Resolving power is good and
contrast is bad
209
Single Focal Length Lenses
EF 15mm f/2.8 Fisheye
1
1
EF 20mm f/2.8 USM
EF 24mm f/1.4L USM
1
0.9
0.9
0.9
0.8
0.8
0.8
0.8
0.7
0.7
0.7
0.7
0.6
0.6
0.6
0.6
0.5
0.5
0.5
0.5
0.4
0.4
0.4
0.4
0.3
0.3
0.3
0.3
0.2
0.2
0.2
0.2
0.1
0.1
0.1
0
0
0
1
5
10
15
EF 24mm f/2.8
0.1
0
20
0
5
10
15
20
EF 28mm f/1.8 USM
1
0
1
5
10
15
20
EF 28mm f/2.8
0
0
1
0.9
0.9
0.9
0.9
0.8
0.8
0.8
0.8
0.7
0.7
0.7
0.7
0.6
0.6
0.6
0.6
0.5
0.5
0.5
0.5
0.4
0.4
0.4
0.4
0.3
0.3
0.3
0.3
0.2
0.2
0.2
0.2
0.1
0.1
0.1
0
0
0
1
5
10
15
EF 35mm f/2
5
10
15
20
EF 50mm f/1.2L USM
1
5
10
15
EF 50mm f/1.4 USM
1
0.9
0.9
0.9
0.8
0.8
0.8
0.8
0.7
0.7
0.7
0.7
0.6
0.6
0.6
0.6
0.5
0.5
0.5
0.5
0.4
0.4
0.4
0.4
0.3
0.3
0.3
0.3
0.2
0.2
0.2
0.2
0.1
0.1
0.1
0
1
5
10
15
EF 85mm f/1.2L@USM
0
5
10
15
EF 85mm f/1.8 USM
1
1
5
10
15
20
EF 100mm f/2 USM
1
0.9
0.9
0.9
0.8
0.8
0.8
0.8
0.7
0.7
0.7
0.7
0.6
0.6
0.6
0.6
0.5
0.5
0.5
0.5
0.4
0.4
0.4
0.4
0.3
0.3
0.3
0.3
0.2
0.2
0.2
0.2
0.1
0.1
0.1
0
0
1
5
10
15
20
EF 135mm f/2.8 (with Softfocus)
5
10
15
20
EF 200mm f/2.8L@USM
1
5
10
15
20
EF 300mm f/2.8L IS USM
0.9
0.9
0.8
0.8
0.8
0.7
0.7
0.7
0.7
0.6
0.6
0.6
0.6
0.5
0.5
0.5
0.5
0.4
0.4
0.4
0.4
0.3
0.3
0.3
0.3
0.2
0.2
0.2
0.2
0.1
0.1
0.1
0.1
0
0
0
1
15
20
0
5
10
15
20
EF 400mm f/4 DO IS USM
EF 400mm f/2.8L IS USM
5
10
15
20
EF 400mm f/5.6L USM
0
1
1
1
0.9
0.9
0.9
0.8
0.8
0.8
0.8
0.7
0.7
0.7
0.7
0.6
0.6
0.6
0.6
0.5
0.5
0.5
0.5
0.4
0.4
0.4
0.4
0.3
0.3
0.3
0.3
0.2
0.2
0.2
0.2
0.1
0.1
0.1
0.1
0
0
0
5
10
15
20
0
5
10
15
20
20
5
15
20
15
20
15
20
10
0
0
0.9
0
15
EF 300mm f/4L IS USM
0.9
10
10
1
0.8
5
5
EF 135mm f/2L USM
0
0.9
0
20
0
0
1
15
0.1
0
0
10
EF 50mm f/1.8@
0
0.9
0
5
0
0
20
20
0.1
0
20
15
EF 35mm f/1.4L USM
0
20
0.9
0
10
0
0
1
5
0.1
0
0
20
0
210
EF 14mm f/2.8L USM
1
0.9
5
10
EF 500mm f/4L IS USM
0
0
5
10
15
20
0
5
10
MTF Characteristics
1
EF 600mm f/4L IS USM
EF 50mm f/2.5 Compact Macro
1
EF 100mm f/2.8 Macro USM
1
1
0.9
0.9
0.9
0.9
0.8
0.8
0.8
0.8
0.7
0.7
0.7
0.7
0.6
0.6
0.6
0.6
0.5
0.5
0.5
0.5
0.4
0.4
0.4
0.4
0.3
0.3
0.3
0.3
0.2
0.2
0.2
0.2
0.1
0.1
0.1
0
0
0
1
5
10
15
MP-E 65mm f/2.8 1-5 x Macro Photo
0.1
0
0
20
5
10
15
20
TS-E 24mm f/3.5L
1
EF 180mm f/3.5L Macro USM
0
0
5
10
15
20
TS-E 45mm f/2.8
1
0
1
0.9
0.9
0.9
0.9
0.8
0.8
0.8
0.8
0.7
0.7
0.7
0.7
0.6
0.6
0.6
0.6
0.5
0.5
0.5
0.5
0.4
0.4
0.4
0.4
0.3
0.3
0.3
0.3
0.2
0.2
0.2
0.2
0.1
0.1
0.1
0
0
0
5
10
15
0
5
10
15
20
10
15
20
10
15
20
TS-E 90mm f/2.8
0.1
0
20
5
0
0
5
10
15
20
0
5
EF-S 60mm f/2.8 Macro USM
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0
5
10
13
Zoom Lenses
WIDE
EF 16-35mm f/2.8L USM
TELE
EF 17-40mm f/4L USM
WIDE
EF135mf/2LUSM
EF 16-35mm f/2.8L USM
1
0.9
0.9
0.9
0.8
0.8
0.8
0.8
0.7
0.7
0.7
0.7
0.6
0.6
0.6
0.6
0.5
0.5
0.5
0.5
0.4
0.4
0.4
0.4
0.3
0.3
0.3
0.3
0.2
0.2
0.2
0.2
0.1
0.1
0.1
0.1
0
0
0
0
5
10
15
EF 20-35mm f/3.5-4.5 USM
20
WIDE
0
5
10
15
EF 20-35mm f/3.5-4.5 USM
1
1
1
0.9
5
10
15
EF 24-70mm f/2.8L USM
TELE
0
20
WIDE
1
1
0.9
0.9
0.9
0.9
0.8
0.8
0.8
0.8
0.7
0.7
0.7
0.7
0.6
0.6
0.6
0.6
0.5
0.5
0.5
0.5
0.4
0.4
0.4
0.4
0.3
0.3
0.3
0.3
0.2
0.2
0.2
0.2
0.1
0.1
0.1
1
0
1
0
0
5
10
15
EF 24-85mm f/3.5-4.5 USM
20
0
WIDE
5
10
15
EF 24-85mm f/3.5-4.5 USM
20
TELE
5
10
15
EF 24-105mm f /4L IS USM
WIDE
1
0.9
0.9
0.8
0.8
0.8
0.8
0.7
0.7
0.7
0.7
0.6
0.6
0.6
0.6
0.5
0.5
0.5
0.5
0.4
0.4
0.4
0.4
0.3
0.3
0.3
0.3
0.2
0.2
0.2
0.2
0.1
0.1
0.1
20
0
5
10
15
20
5
10
15
20
TELE
1
0.1
0
0
15
20
TELE
EF 24-105mm f /4L IS USM
1
10
15
EF 24-70mm f/2.8L USM
0
20
0.9
5
10
0
0
1
0
5
0.1
0
0.9
0
TELE
0
0
20
EF 17-40mm f/4L USM
0
5
10
15
20
0
0
5
10
15
20
211
Zoom Lenses
EF 28-90mm f/4-5.6@USM
WIDE
EF 28-90mm f/4-5.6@USM
EF 28-90mm f/4-5.6#
EF 28-90mm f/4-5.6#
WIDE
1
1
1
0.9
0.9
0.9
0.8
0.8
0.8
0.8
0.7
0.7
0.7
0.7
0.6
0.6
0.6
0.6
0.5
0.5
0.5
0.5
0.4
0.4
0.4
0.4
0.3
0.3
0.3
0.3
0.2
0.2
0.2
0.2
0.1
0.1
0.1
0
5
10
15
EF 28-105mm f/3.5-4.5@USM
1
0
20
WIDE
1
5
10
15
EF 28-105mm f/3.5-4.5@USM
TELE
0
0
20
5
10
15
20
0
EF 28-105mm f/4-5.6 USM / EF 28-105mm f/4-5.6 WIDE
1
0.9
0.9
0.9
0.8
0.8
0.8
0.8
0.7
0.7
0.7
0.7
0.6
0.6
0.6
0.6
0.5
0.5
0.5
0.5
0.4
0.4
0.4
0.4
0.3
0.3
0.3
0.3
0.2
0.2
0.2
0.2
0.1
0.1
0.1
0
0
1
5
10
15
EF 28-135mm f/3.5-5.6 IS USM
0
20
WIDE
1
5
10
15
EF 28-135mm f/3.5-5.6 IS USM
20
TELE
5
10
15
20
0
EF 28-200mm f/3.5-5.6 USM / EF 28-200mm f/3.5-5.6 WIDE
0.9
0.8
0.8
0.8
0.8
0.7
0.7
0.7
0.7
0.6
0.6
0.6
0.6
0.5
0.5
0.5
0.5
0.4
0.4
0.4
0.4
0.3
0.3
0.3
0.3
0.2
0.2
0.2
0.2
0.1
0.1
0.1
0
0
0
15
0
20
EF 28-300mm f/3.5-5.6L IS USM WIDE
5
10
15
EF 28-300mm f/3.5-5.6L IS USM TELE
5
10
15
EF 55-200mm f/4.5-5.6 @ USM
20
WIDE
0
1
1
1
1
0.9
0.9
0.9
0.8
0.8
0.8
0.8
0.7
0.7
0.7
0.7
0.6
0.6
0.6
0.6
0.5
0.5
0.5
0.5
0.4
0.4
0.4
0.4
0.3
0.3
0.3
0.3
0.2
0.2
0.2
0.2
0.1
0.1
0.1
0.1
0
0
0
5
10
15
EF 70-200mm f/2.8L IS USM
20
0
WIDE
5
10
15
EF 70-200mm f/2.8L IS USM
TELE
5
10
15
EF 70-200mm f/2.8L USM
20
WIDE
1
1
1
0.9
0.9
0.9
0.9
0.8
0.8
0.8
0.8
0.7
0.7
0.7
0.7
0.6
0.6
0.6
0.6
0.5
0.5
0.5
0.5
0.4
0.4
0.4
0.4
0.3
0.3
0.3
0.3
0.2
0.2
0.2
0.2
0.1
0.1
0.1
0.1
0
0
0
0
1
5
10
15
EF 70-200mm f/4L IS USM
20
WIDE
0
1
5
10
15
EF 70-200mm f/4L IS USM
TELE
1
1
5
10
15
EF 70-200mm f/4L USM
20
WIDE
0.9
0.8
0.8
0.8
0.8
0.7
0.7
0.7
0.7
0.6
0.6
0.6
0.6
0.5
0.5
0.5
0.5
0.4
0.4
0.4
0.4
0.3
0.3
0.3
0.3
0.2
0.2
0.2
0.2
0.1
0.1
0.1
0
10
15
20
5
10
15
20
20
5
10
15
EF 70-200mm f/2.8L USM
TELE
5
10
15
20
TELE
0.1
0
0
20
0
EF 70-200mm f/4L USM
0.9
5
15
1
0.9
0
10
TELE
0
0.9
0
5
EF 55-200mm f/4.5-5.6 @ USM
0
0
20
20
0
0
20
15
0
0.9
0
10
0.1
0
20
5
EF 28-200mm f/3.5-5.6 USM / EF 28-200mm f/3.5-5.6 TELE
0.9
10
20
1
0.9
5
15
0
0
0.9
0
10
0.1
0
1
5
EF 28-105mm f/4-5.6 USM / EF 28-105mm f/4-5.6 TELE
1
0.9
0
TELE
0.1
0
0
0
212
TELE
1
0.9
0
0
5
10
15
20
0
5
10
15
20
MTF Characteristics
EF 70-300mm f/4-5.6 IS USM
1
WIDE
EF 70-300mm f/4-5.6 IS USM
1
EF 70-300mm f/4.5-5.6 DO IS USM WIDE
TELE
EF 70-300mm f/4.5-5.6 DO IS USM TELE
1
1
0.9
0.9
0.9
0.9
0.8
0.8
0.8
0.8
0.7
0.7
0.7
0.7
0.6
0.6
0.6
0.6
0.5
0.5
0.5
0.5
0.4
0.4
0.4
0.4
0.3
0.3
0.3
0.3
0.2
0.2
0.2
0.2
0.1
0.1
0.1
0
0
0
5
10
15
20
EF 75-300mm f/4-5.6#USM / EF 75-300mm f/4-5.6# WIDE
1
0
5
10
15
0
0
EF 75-300mm f/4-5.6#USM / EF 75-300mm f/4-5.6# TELE
1
0.1
0
20
1
5
10
15
EF 80-200mm f/4.5-5.6@
0
20
WIDE
1
0.9
0.9
0.9
0.9
0.8
0.8
0.8
0.8
0.7
0.7
0.7
0.7
0.6
0.6
0.6
0.6
0.5
0.5
0.5
0.5
0.4
0.4
0.4
0.4
0.3
0.3
0.3
0.3
0.2
0.2
0.2
0.2
0.1
0.1
0.1
0
0
0
5
10
15
EF 90-300mm f/4.5-5.6 USM / EF 90-300mm f/4.5-5.6 WIDE
5
10
15
20
EF 90-300mm f/4.5-5.6 USM / EF 90-300mm f/4.5-5.6 TELE
5
10
15
EF 100-300mm f/4.5-5.6 USM
WIDE
1
1
1
0.9
0.9
0.9
0.8
0.8
0.8
0.8
0.7
0.7
0.7
0.7
0.6
0.6
0.6
0.6
0.5
0.5
0.5
0.5
0.4
0.4
0.4
0.4
0.3
0.3
0.3
0.3
0.2
0.2
0.2
0.2
0.1
0.1
0.1
0
0
0
10
15
20
0
EF 100-400mm f/4.5-5.6L IS USM WIDE
5
10
15
EF 100-400mm f/4.5-5.6L IS USM TELE
1
1
1
10
15
EF-S 10-22mm f/3.5-4.5 USM
WIDE
1
0.9
0.9
0.8
0.8
0.7
0.7
0.9
0.8
0.7
0.7
0.6
0.6
0.6
0.6
0.5
0.5
0.5
0.5
0.4
0.4
0.4
0.4
0.3
0.3
0.3
0.3
0.2
0.2
0.2
0.2
0.1
0.1
0.1
0.1
0
0
0
10
15
EF-S 17-55mm f/2.8 IS USM
20
0
WIDE
5
10
15
EF-S 17-55mm f/2.8 IS USM
TELE
5
10
13
EF-S 17-85mm f/4-5.6 IS USM
WIDE
1
1
1
0.9
0.9
0.9
0.8
0.8
0.8
0.8
0.7
0.7
0.7
0.7
0.6
0.6
0.6
0.6
0.5
0.5
0.5
0.5
0.4
0.4
0.4
0.4
0.3
0.3
0.3
0.3
0.2
0.2
0.2
0.2
0.1
0.1
0.1
0.1
0
0
1
5
10
13
EF-S 18-55mm f/3.5-5.6@ USM / EF-S 18-55mm f/3.5-5.6@ WIDE
0
1
0.9
0.9
0.8
0.8
0.7
0.7
0.6
0.6
0.5
0.5
0.4
0.4
0.3
0.3
0.2
0.2
10
13
20
TELE
10
15
20
TELE
0
5
10
1
5
10
EF-S 17-85mm f/4-5.6 IS USM
13
TELE
0
0
5
10
EF-S 18-55mm f/3.5-5.6@ USM / EF-S 18-55mm f/3.5-5.6@ TELE
0.1
0.1
0
5
5
EF-S 10-22mm f/3.5-4.5 USM
0
0.9
0
0
15
0
0
20
10
EF 100-300mm f/4.5-5.6 USM
0
20
0.8
5
5
0
5
0.9
0
TELE
0.1
0
20
20
EF 80-200mm f/4.5-5.6@
0
20
1
5
15
0
0
0.9
0
10
0.1
0
0
20
5
0
0
5
10
13
0
5
10
13
213
Extenders
EF 1.4x@
EF 70-200mm f/2.8L IS USM
WIDE
EF 70-200mm f/2.8L IS USM
EF 70-200mm f/2.8L USM
WIDE
EF 70-200mm f/2.8L USM
1
1
1
0.9
0.9
0.9
0.9
0.8
0.8
0.8
0.8
0.7
0.7
0.7
0.7
0.6
0.6
0.6
0.6
0.5
0.5
0.5
0.5
0.4
0.4
0.4
0.4
0.3
0.3
0.3
0.3
0.2
0.2
0.2
0.2
0.1
0.1
0.1
0.1
0
0
0
0
5
10
EF 70-200mm f/4 IS USM
15
20
0
WIDE
5
10
EF 70-200mm f/4 IS USM
15
TELE
5
10
15
EF 70-200mm f/4L USM
20
0
1
1
0.9
0.9
0.9
0.9
0.8
0.8
0.8
0.8
0.7
0.7
0.7
0.7
0.6
0.6
0.6
0.6
0.5
0.5
0.5
0.5
0.4
0.4
0.4
0.4
0.3
0.3
0.3
0.3
0.2
0.2
0.2
0.2
0.1
0.1
0.1
0.1
0
0
0
10
15
EF 100-400mm f/4.5-5.6L IS USM
20
0
5
10
15
EF 100-400mm f/4.5-5.6L IS USM (—:f/16) TELE
WIDE
5
10
15
20
0
EF 135mm f/2L USM
1
1
1
0.9
0.9
0.9
0.9
0.8
0.8
0.8
0.8
0.7
0.7
0.7
0.7
0.6
0.6
0.6
0.6
0.5
0.5
0.5
0.5
0.4
0.4
0.4
0.4
0.3
0.3
0.3
0.3
0.2
0.2
0.2
0.2
0.1
0.1
0.1
0
0
5
10
15
20
EF 200mm f/2.8L@USM
5
10
15
20
5
10
15
20
0
EF 300mm f/4L IS USM
1
1
1
0.9
0.9
0.9
0.8
0.8
0.8
0.8
0.7
0.7
0.7
0.7
0.6
0.6
0.6
0.6
0.5
0.5
0.5
0.5
0.4
0.4
0.4
0.4
0.3
0.3
0.3
0.3
0.2
0.2
0.2
0.2
0.1
0.1
0.1
0.1
0
0
0
5
10
15
20
0
5
10
15
5
10
15
0
20
EF 500mm f/4L IS USM
1
1
1
0.9
0.9
0.9
0.9
0.8
0.8
0.8
0.8
0.7
0.7
0.7
0.7
0.6
0.6
0.6
0.6
0.5
0.5
0.5
0.5
0.4
0.4
0.4
0.4
0.3
0.3
0.3
0.3
0.2
0.2
0.2
0.2
0.1
0.1
0.1
0.1
0
0
0
5
10
15
20
0
5
10
15
20
15
20
5
10
15
20
5
10
15
20
15
20
EF 600mm f/4L IS USM
1
0
10
0
0
(—:f/16)
EF 400mm f/5.6L USM
EF 400mm f/4 DO IS USM
20
5
EF 400mm f/2.8L IS USM
1
0.9
0
TELE
0
0
EF 300mm f/2.8L IS USM
20
0.1
0
0
15
EF 180mm f/3.5L Macro USM
1
0
10
0
0
20
5
EF 70-200mm f/4L USM
WIDE
1
5
TELE
0
0
20
1
0
214
TELE
1
0
0
5
10
15
20
0
5
10
MTF Characteristics
EF 2x@
EF 70-200mm f/2.8L IS USM
WIDE
EF 70-200mm f/2.8L IS USM
TELE
EF 70-200mm f/2.8L USM
WIDE
EF 70-200mm f/2.8L USM
1
1
1
1
0.9
0.9
0.9
0.9
0.8
0.8
0.8
0.8
0.7
0.7
0.7
0.7
0.6
0.6
0.6
0.6
0.5
0.5
0.5
0.5
0.4
0.4
0.4
0.4
0.3
0.3
0.3
0.3
0.2
0.2
0.2
0.2
0.1
0.1
0.1
0.1
0
0
0
0
5
10
EF 70-200mm f/4 IS USM
15
20
0
WIDE
5
10
EF 70-200mm f/4 IS USM
15
0
0
20
5
10
15
20
0
EF 70-200mm f/4L USM (—:f/16) WIDE
TELE
1
1
1
0.9
0.9
0.9
0.9
0.8
0.8
0.8
0.8
0.7
0.7
0.7
0.7
0.6
0.6
0.6
0.6
0.5
0.5
0.5
0.5
0.4
0.4
0.4
0.4
0.3
0.3
0.3
0.3
0.2
0.2
0.2
0.2
0.1
0.1
0.1
0.1
0
0
5
10
15
20
0
0
EF 100-400mm f/4.5-5.6L IS USM (—:f/22) WIDE
5
10
15
20
5
10
15
0
20
1
1
1
0.9
0.9
0.9
0.8
0.8
0.8
0.8
0.7
0.7
0.7
0.7
0.6
0.6
0.6
0.6
0.5
0.5
0.5
0.5
0.4
0.4
0.4
0.4
0.3
0.3
0.3
0.3
0.2
0.2
0.2
0.2
0.1
0.1
0.1
0.1
0
0
0
5
10
15
0
20
EF 200mm f/2.8L@USM
5
10
15
5
10
15
20
0
(—:f/16)
EF 300mm f/4L IS USM
EF 300mm f/2.8L IS USM
1
1
1
0.9
0.9
0.9
0.9
0.8
0.8
0.8
0.8
0.7
0.7
0.7
0.7
0.6
0.6
0.6
0.6
0.5
0.5
0.5
0.5
0.4
0.4
0.4
0.4
0.3
0.3
0.3
0.3
0.2
0.2
0.2
0.2
0.1
0.1
0.1
0.1
0
0
0
5
10
15
0
20
(—:f/16)
EF 400mm f/4 DO IS USM
5
10
15
(—:f/22)
EF 400mm f/5.6L USM
5
10
15
0
20
(—:f/16)
EF 500mm f/4L IS USM
1
1
0.9
0.9
0.9
0.9
0.8
0.8
0.8
0.8
0.7
0.7
0.7
0.7
0.6
0.6
0.6
0.6
0.5
0.5
0.5
0.5
0.4
0.4
0.4
0.4
0.3
0.3
0.3
0.3
0.2
0.2
0.2
0.2
0.1
0.1
0.1
0
0
5
10
15
20
5
10
15
20
15
20
(—:f/16)
5
10
15
20
5
10
15
20
(—:f/16)
0.1
0
0
0
10
EF 600mm f/4L IS USM
1
0
5
0
0
20
TELE
EF 400mm f/2.8L IS USM
1
0
20
0
0
20
15
EF 180mm f/3.5L Macro USM
EF 135mm f/2L USM
1
0.9
0
10
0
0
EF 100-400mm f/4.5-5.6L IS USM (—:f/22) TELE
5
EF 70-200mm f/4L USM (—:f/16)
1
0
TELE
0
5
10
15
20
0
5
10
15
20
215
EF LENS WORK III
The Eyes of EOS
September 2006, Eighth edition
Publisher and Planning Canon Inc. Lens Products Group
Production and Editorial Canon Inc. Lens Products Group
Printer
Nikko Graphic Arts Co., Ltd.
Thanks for the Cooperation of : Brasserie Le Solférino/Restaurant de la Maison Fouraise,
Chatou/
Hippodrome de Marseille Borély/Cyrille Varet Créations, Paris/Jean
Pavie, artisan luthier, Paris/Participation de la Mairie de Paris/JeanMichel OTHONIEL, sculpteur
©Canon Inc. 2003
Products and specifications are subject to change without notice.
The photographs in this book are the property of Canon Inc., or used with the permission of the photographer.
CANON INC.
30-2, Shimomaruko 3-chome, Ohta-ku, Tokyo 146-8501, Japan